Apparatus and method for delivering a treatment liquid and ozone to treat the surface of a workpiece

ABSTRACT

An apparatus for supplying a mixture of a treatment liquid and ozone for treatment of a surface of a workpiece, and a corresponding method are set forth The preferred embodiment of the apparatus comprises a liquid supply line that is used to provide fluid communication between a reservoir containing the treatment liquid and a treatment chamber housing the workpiece. A heater is disposed to heat the workpiece, either directly or indirectly. Preferably, the workpiece is heated by heating the treatment liquid that is supplied to the workpiece. One or more nozzles accept the treatment liquid from the liquid supply line and spray it onto the surface of the workpiece while an ozone generator provides ozone into an environment containing the workpiece.

BACKGROUND OF THE INVENTION

[0001] The importance of clean semiconductor workpiece surfaces in thefabrication of semiconductor microelectronic devices has been recognizedfor a considerable period of time. Over time, as VLSI and ULSI siliconcircuit technology has developed, the cleaning processes have graduallybecome a particularly critical step in the fabrication process. It hasbeen estimated that over 50% of the yield losses sustained in thefabrication process are a direct result of workpiece contaminants. Traceimpurities, such as sodium ions, metals, and particles, are especiallydetrimental if present on semiconductor surfaces during high-temperatureprocessing because they may spread and diffuse into the semiconductorworkpiece and thereby alter the electrical characteristics of thedevices formed in the workpiece. Similar requirements are placed onother such items in the electronics industry, such as in the manufactureof flat panel displays, hard disk media, CD glass, and other suchworkpieces.

[0002] Cleaning of a semiconductor workpiece, and other electronicworkpieces, occurs at many intermediate stages of the fabricationprocess. Cleaning of the workpiece is often critical after, for example,photoresist stripping and/or ashing. This is particularly true where thestripping and/or ashing process immediately proceeds a thermal process.Complete removal of the ashed photoresist or the photoresistst/stripperis necessary to insure the integrity of subsequent processes.

[0003] The actual stripping of photoresist from the workpiece is yetanother fabrication process that is important to integrated circuityield, and the yield of other workpiece types. It is during thestripping process that a substantial majority of the photoresist isremoved or otherwise disengaged from the surface of the semiconductorworkpiece. If the stripping agent is not completely effective,photoresist may remain bonded to the surface. Such bonded photoresistmay be extremely difficult to remove during a subsequent cleaningoperation and thereby impact the ability to further process theworkpiece.

[0004] Various techniques are used for stripping photoresist from thesemiconductor workpiece. Mixtures of sulfuric acid and hydrogen peroxideat elevated temperatures are commonly used. However, such mixtures areunsuitable for stripping photoresist from wafers on which metals, suchas aluminum or copper, have been deposited. This is due to the fact thatsuch solutions will attack the metals as well as the photoresist.Solvent chemistries are often used after metal layers have beendeposited. In either case, limited bath life, expensive chemistries, andhigh waste disposal costs have made alternative strip chemistriesattractive.

[0005] Plasma stripping systems provide such an alternative and havebeen used for stripping both pre- and post-metal photoresist layers.This stripping technique, however, does not provide an ideal solutiondue to the high molecular temperatures generated at the semiconductorworkpiece surface. Additionally, since photoresist is not purely ahydrocarbon (i.e., it generally contains elements other than hydrogenand carbon), residual compounds may be left behind after the plasmastrip. Such residual compounds must then the removed in a subsequent wetclean.

[0006] Ozone has been used in various applications in the semiconductorindustry for a number of years. Often, the ozone is combined withdeionized water to form an effective treatment solution. The attractivefeatures of such a solution include low-cost, repeatable processing,minimal attack on underlying device layers, and the elimination of wastestreams that must be treated before disposal. The main drawback withusing such solutions has been the slow reaction rates that translateinto long process times and flow throughput.

[0007] Photoresist strip using ozone dissolved in water has beensomewhat more successful in achieving viable process rate at acceptableprocess temperatures. However, ozone, like all gases, has a limitedsolubility in aqueous solutions. At temperatures near ambient, ozonesaturation occurs at around 20 ppm. Ozone solubility in water increasesdramatically with decreasing temperature, to a maximum of a little over100 ppm at temperatures approaching 0 degrees Celsius and drops toalmost zero at temperatures approaching 60 degrees Celsius. Whileincreasing ozone concentration increases the kinetic reaction rate, adecrease in temperature simultaneously suppresses that rate.

[0008] A technique for stripping photoresist and/or cleaning asemiconductor workpiece using ozone and deionized water is set forth inU.S. Pat. No. 5,464,480, titled “Process and Apparatus for the Treatmentof Semiconductor Wafers in a Fluid”, issued Nov. 7, 1995. The '480patent purports to set forth a method and apparatus in whichlow-temperature deionized water is ozonated by bubbling ozone throughthe low-temperature water. The low-temperature, ozonated, deionizedwater is in the form of a bath. Semiconductor wafers are batch processedby immersing the wafers in the bath, for example, to clean the wafers,strip photoresist, etc.

[0009] The present inventors have found that the foregoing systempurportedly described in the '480 patent may not be optimal for use inmany circumstances. Static boundary regions between the bath and thesurface of the semiconductor workpiece may result in sub-optimalcleaning and/or stripping. Finally, ozone concentration in the deionizedwater bath may be difficult to maintain in view of the fact that theapparatus of the '480 patent is an open atmospheric system.

BRIEF SUMMARY OF THE INVENTION

[0010] An apparatus for supplying a mixture of a treatment liquid andozone for treatment of a surface of a workpiece, such as a semiconductorworkpiece, and a corresponding method are set forth. The preferredembodiment of the apparatus comprises a liquid supply line that is usedto provide fluid communication between a reservoir containing thetreatment liquid and a treatment chamber housing the semiconductorworkpiece. A heater is disposed to heat the workpiece, either directlyor indirectly. Preferably, the workpiece is heated by heating thetreatment liquid that is supplied to the workpiece. One or more nozzlesaccept the treatment liquid from the liquid supply line and spray itonto the surface of the workpiece while an ozone generator providesozone into an environment containing the workpiece.

[0011] Generally, a heated treatment liquid is ill suited for dissolvingozone therein As such, a thick boundary layer of treatment fluiddisposed on the surface of the workpiece may act to inhibit the abilityof the ozone to reach and react with the components that are, forexample, to be removed from the surface of the workpiece. The apparatustherefore preferably includes one or more processing components that areused to control the thickness of the boundary layer of the heatedtreatment liquid on the surface of the workpiece. Reducing the thicknessof the boundary layer facilitates diffusion of the ozone through theboundary layer to the surface of the workpiece. Significantly increasedcleaning and stripping rates have been observed in such an apparatus,particularly when the treatment liquid is a water-containing liquid suchas deionized water.

[0012] In accordance with a preferred method for treating a workpiece,the workpiece is first heated. A treatment liquid is provided to thesurface of the workpiece that is to be treated and an amount of ozone isintroduced into an environment containing the workpiece. Even morepreferably, the thickness of a liquid boundary layer on the surface ofthe semiconductor workpiece is controlled to allow diffusion of theozone therethrough so that the ozone may react at the surface of theworkpiece.

[0013] In accordance with yet another embodiment of the apparatus, theapparatus comprises a liquid reservoir having a liquid chamber, a pumphaving an input in fluid communication with the liquid chamber and anoutput in fluid communication with one or more nozzles disposed to sprayfluid therefrom onto the surface of the workpiece. A fluid path extendsbetween the output of the pump and the nozzle and carries thepressurized liquid that is provided at the output of the pump. An ozonesupply system injects ozone into the fluid path. As such, a pressurizedmixture of treatment liquid and ozone is sprayed onto the surface of thesemiconductor workpiece to thereby eliminate many of the problemsassociated with prior systems. A method for treating a workpiece in themanner exercised by the foregoing apparatus system is also disclosed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0014]FIG. 1 is a schematic block diagram of one embodiment of anapparatus for treating a semiconductor workpiece in which ozone isinjected into a line containing a pressurized treatment liquid.

[0015]FIG. 2 is a schematic block diagram of one embodiment of anapparatus for treating a semiconductor workpiece in which thesemiconductor workpiece is indirectly heated by heating a treatmentliquid that is sprayed on the surface of the workpiece.

[0016]FIG. 3 is a flow diagram illustrating one embodiment of a processflow for treating a semiconductor workpiece with a treatment fluid andozone.

[0017]FIG. 4 is a schematic block diagram of an alternative embodimentof the system set forth in FIG. 2 wherein the ozone and treatment fluidare provided to the semiconductor workpiece along different flow paths.

[0018]FIG. 5 is a schematic block diagram of an embodiment of anapparatus for treating a semiconductor workpiece in which pressurizedsteam and ozone are provided in a pressurized chamber containing asemiconductor workpiece.

[0019]FIG. 6 is a schematic block diagram of an embodiment of anapparatus for treating a semiconductor workpiece in which anultra-violet lamp is used to enhance the kinetic reactions at thesurface of the workpiece.

DETAILED DESCRIPTION OF THE INVENTION

[0020] One embodiment of an apparatus suitable for providing ozone and atreatment liquid for treatment of a semiconductor workpiece isillustrated in FIG. 1. The treatment system, shown generally at 10,includes a treatment chamber 15 that contains one or more workpieces 20,such as semiconductor wafer workpieces. Although the illustrated systemis directed to a batch workpiece apparatus, it will be recognized thatthe system is readily adaptable for use in single workpiece processingas well.

[0021] The semiconductor workpieces 20 are supported within the chamber15 by one or more supports 25 extending from, for example, a rotorassembly 30. Rotor assembly 30 seals with the housing of the treatmentchamber 15 to form a sealed, closed processing environment. Further,rotor assembly 30 is provided so that the semiconductor workpieces 20may be spun about axis 35 during or after treatment with the ozone andtreatment liquid.

[0022] One or more nozzles 40 are disposed within the treatment chamber15 so as to direct a spray mixture of ozone and treatment liquid ontothe surfaces of the semiconductor workpieces 20 that are to be treated.In the illustrated embodiment, the nozzles 40 direct a spray oftreatment fluid to the underside of the semiconductor workpieces 20.However, it will be recognized that the fluid spray may be directedalternatively, or in addition, to the upper surface of the semiconductorworkpieces 20.

[0023] Treatment liquid and ozone are supplied to the nozzles 40 withthe assistance of a number of system components that are uniquelyarranged to provide a single fluid line comprising ozone mixed with thetreating liquid. To this end, a reservoir 45 defines a chamber 50 inwhich the liquid that is to be mixed with the ozone is stored. Thechamber 50 is in fluid communication with the input of a pump mechanism55. The pump mechanism 55 provides the liquid under pressure along afluid flow path, shown generally at 60, for ultimate supply to the inputof the nozzles 40. The preferred treatment fluid is deionized water, butit will be recognized that other treatment fluids, such as other aqueousor non-aqueous solutions, may also be employed.

[0024] A number of components are disposed along the fluid flow path 60.First, a filter 65 is disposed along the fluid flow path 60 to filterout microscopic contaminants from the treatment fluid. The treatmentfluid, still under pressure, is provided at the output of the filter 65along fluid flow line 70. It is along fluid flow line 70 that ozone isinjected. The ozone is generated by ozone generator 75 and is suppliedalong fluid flow line 80 under pressure to fluid flow line 70.Optionally, the treatment liquid, now injected with ozone, is suppliedto the input of a mixer 90 that mixes the ozone and the treatmentliquid. The mixer 90 may be static or active. From the mixer 90, thetreatment liquid and ozone are provided to be input of nozzles 40 which,in turn, spray the liquid on the surface of the semiconductor workpieces20 that are to be treated and, further, introduce the ozone into theenvironment of the treatment chamber 15.

[0025] To further concentrate the ozone in the treatment liquid, anoutput of the ozone generator 75 may be supplied to a dispersion unit 95disposed in the liquid chamber 50 of the reservoir 45. The dispersionunit 95 provides a dispersed flow of ozone through the treatment liquidto thereby add ozone to the fluid stream prior to injection of a furtheramount of ozone along the fluid path 60.

[0026] In the embodiment of the system of FIG. 1, spent liquid inchamber 15 is provided along fluid line 105 to, for example, a valvemechanism 110. The valve mechanism 110 may be operated to provide thespent liquid to either a drain output 115 or back to the liquid chamber50 of the reservoir 45. Repeated cycling of the treatment liquid throughthe system and back to the reservoir 45 assists in elevating the ozoneconcentration in the liquid through repeated ozone injection and/orozone dispersion.

[0027] A further embodiment of a system for delivering a fluid mixturefor treating the surface of a semiconductor workpiece is illustrated inFIG. 2. Although the system 120 of FIG. 2 appears to be substantiallysimilar to the system 10 of FIG. 1, there are significant differences.The system 120 of FIG. 2 is based upon the recognition by the presentinventors that the heating of the surfaces of the semiconductorworkpieces 20 with a heated liquid that is supplied along with a flow ofozone that creates an ozonated atmosphere is highly effective inphotoresist stripping, ash removal, and/or cleaning processes. As such,system 120 includes one or more heaters 125 that are used to heat thetreatment liquid so that it is supplied to the surfaces of thesemiconductor workpieces at an elevated temperature that accelerates thesurface reactions. It will be recognized that it is also possible todirectly heat the workpieces so as to stimulate the reactions. Suchheating may take place in addition to or instead of the indirect heatingof the workpieces through contact with the heated treatment liquid. Forexample, supports 25 may include heating elements that may be used toheat the workpieces 20. The chamber 15 may include a heater forelevating the temperature of the chamber environment and workpieces.

[0028] As noted above, the preferred treatment liquid is deionized watersince it is believed to be required to initiate the cleaning/removalreactions at the workpiece surface, probably through hydrolysis of thecarbon-carbon bonds of organic molecules. The present inventors,however, recognize that significant amounts of water can form acontinuous film on the semiconductor workpiece surface. This film actsas a diffusion barrier to the ozone, thereby inhibiting reaction rates.Control of the boundary layer thickness, as will be explained in furtherdetail below, is implemented by control of the rpm of the semiconductorworkpiece, vapor delivery, and controlled spraying of the treatmentliquid, or a combination of one or more of these techniques. By reducingthe boundary layer thickness, the ozone is allowed to diffuse to thesurface of the workpieces and react with the organic materials that areto be removed.

[0029]FIG. 3 illustrates one embodiment of a process that may beimplemented in the system of FIG. 2 when the system 120 is used, forexample, to strip photoresist from the surfaces of semiconductorworkpieces. At step 200, the workpieces 20 that are to be stripped areplaced in, for example, a Teflon wafer cassette. This cassette is placedin a closed environment, such as in chamber 15. Chamber 15 and itscorresponding components may be constructed based on a spray solventtool platform or spray acid tool platform such as those available fromSemitool, Inc., of Kalispell, Mont. Alternatively, the semiconductorworkpieces 20 may be disposed in chamber 15 in a carrierless manner,consistent with the automated processing platform design of the MAGNUM®brand semiconductor processing tool available from Semitool, Inc.

[0030] At step 205, heated deionized water is sprayed onto the surfacesof the semiconductor workpieces 20. The heated deionized water heats thesurfaces of the semiconductor workpieces 20 as well as the enclosedenvironment of the chamber 15. When the spray is discontinued, a thinliquid film remains on the workpiece surfaces. If the surface ishydrophobic, a surfactant may be added to the deionized water to assistin creating a thin liquid boundary layer on the workpiece surfaces.

[0031] The surface boundary layer of deionized water is controlled atstep 210 using one or more techniques. For example, the semiconductorworkpieces 20 may be rotated about axis 35 by rotor 30 to therebygenerate centripetal accelerations that thin the boundary layer. Theflow rate of the deionized water may also be used to control thethickness of the surface boundary layer. Lowering of the flow rateresults in decreased boundary layer thickness. Still further, the mannerin which the deionized water is injected into the chamber 15 may be usedto control the boundary layer thickness. Nozzles 40 may be designed toprovide the deionized water as micro-droplets thereby resulting in athin boundary layer.

[0032] At step 215, ozone is injected into the fluid flow path 60 duringthe water spray, or otherwise provided to the internal chamberenvironment of chamber 15. If the apparatus of FIG. 2 is utilized, theinjection of the ozone continues after the spray has shut off. If theworkpiece surface begins to dry, a brief spray is preferably activatedto replenish the liquid film on the workpiece surface. This ensures thatthe exposed workpiece surfaces remain wetted at all times and, further,ensures that the workpiece temperature is and remains elevated at thedesired reaction temperature. It has been found that a continuous sprayof deionized water having a flow rate that is sufficient to maintain theworkpiece surfaces at an elevated temperature, and high rotationalspeeds (i.e.,>300 rpm, between 300 and 800 rpm, or even as high as orgreater than 1500 rpm) generates a very thin boundary layer whichminimizes the ozone diffusion barrier and thereby leads to an enhancedphotoresist stripping rate. As such, the control of the boundary layerthickness is used to regulate the diffusion of reactive ozone to thesurface of the wafer.

[0033] While ozone has a limited solubility in the heated deionizedwater, the ozone is able to diffuse through the water and react withphotoresist at the liquid/resist interface. It is believed that thepresence of the deionized water itself further assists in the reactionsby hydrolyzing the carbon-carbon bonds of organic deposits, such asphotoresist, on the surface of the wafer. The higher temperaturepromotes the reaction kinetics while the high concentration of ozone inthe gas phase promotes diffusion of ozone through the boundary layerfilm even though the high temperature of the boundary layer film doesnot actually have a high concentration of dissolved ozone.

[0034] After the semiconductor workpieces 20 have been processed throughthe reactions of the ozone and/or liquid with the materials to theremoved, the workpieces are subject to a rinse at 220 and are dried atstep 225. For example, the workpieces may be sprayed with a flow ofdeionized water during the rinse at step 220. They may then be subjectto any one or more known drying techniques thereafter at step 225.

[0035] With reference to FIG. 4, there is shown yet a further embodimentof the ozone treatment system 227. In the embodiment of FIG. 4, one ormore nozzles 230 are disposed within the treatment chamber 15 to conductozone from ozone generator 75 directly into the reaction environment.The heated treatment fluid is provided to the chamber 15 through nozzles40 that receive the treatment fluid, such as heated deionized water,through a supply line that is separate from the ozone supply line. Assuch, injection of ozone in fluid path 60 is optional.

[0036] Another embodiment of an ozone treatment system is showngenerally at 250 in FIG. 5. In the system 250, a steam boiler 260 thatsupplies saturated steam under pressure to the process chamber 15 hasreplaced the pump mechanism The reaction chamber 15 is preferably sealedto thereby form a pressurized atmosphere for the reactions. For example;saturated steam at 126 degrees Celsius could be generated by steamboiler 260 and supplied to reaction chamber 15 to generate a pressure of35 psia therein during the workpiece processing. Ozone may be directlyinjected into the chamber 15 as shown, and/or may be injected into thepath 60 for concurrent supply with the steam. Using the systemarchitecture of this embodiment, it is thus possible to achievesemiconductor workpiece surface temperatures in excess of 100 degreesCelsius, thereby further accelerating the reaction kinetics.

[0037] A still further enhancement that may be made to any one of theforegoing systems is illustrated in FIG. 6. In this embodiment, anultra-violet lamp 300 is used to irradiate the surface of thesemiconductor workpiece 20 during processing. Such irradiation furtherenhances the reaction kinetics. Although this irradiation technique isapplicable to batch semiconductor workpiece processing, it is moreeasily and economically implemented in the illustrated single waferprocessing environment where the workpiece is more easily completelyexposed to the UV radiation.

[0038] The presently disclosed apparatus and methods may be used totreat workpieces beyond the semiconductor workpieces described above.For example, other workpieces, such as flat panel displays, hard diskmedia, CD glass, etc, may also be have their surfaces treated using theforegoing apparatus and methods.

[0039] Although the preferred treatment liquid for the disclosedapplication is deionized water, other treatment liquids may also beused. For example, acidic and basic solutions may be used, depending onthe particular surface to be treated and the material that is to beremoved. Treatement liquids comprising sulfuric acid, hydrochloric acid;and ammonium hydroxide may be useful in various applications.

[0040] Numerous modifications may be made to the foregoing systemwithout departing from the basic teachings thereof. Although the presentinvention has been described in substantial detail with reference to oneor more specific embodiments, those of skill in the art will recognizethat changes may be made thereto without departing from the scope andspirit of the invention as set forth in the appended claims.

1. A method for treating a workpiece comprising the steps of: (a)contacting a workpiece having a thin aqueous liquid boundary layer onthe surface thereof with ozone whereby the ozone can diffuse through theboundary layer to provide a diffusion-controlled reaction between theozone and the surface of the workpiece, and (b) reacting the ozone withthe surface of the workpiece while the surface of workpiece is at anelevated temperature.
 2. A method as defined in claim 1 wherein the thinaqueous liquid boundary layer is established on the surface of theworkpiece by spraying aqueous liquid onto said surface and rotating theworkpiece at a speed of rotation sufficient to control the thickness ofthe boundary layer.
 3. A method as defined in claim 1 wherein the thinaqueous liquid boundary layer is established on the surface of theworkpiece by supplying aqueous liquid in vapor form whereby the vaporcondenses on the surface of the workpiece to form a thin aqueous liquidboundary layer thereon.
 4. A method as defined in claim 1 wherein thethin aqueous liquid boundary layer is established by spraying a mixtureof ozone and aqueous liquid onto the surface of the workpiece wherebythe ozone separates from said aqueous liquid as the aqueous liquid formssaid boundary layer.
 5. A method as defined in claim 1 wherein theworkpiece is maintained at an elevated temperature by heating theworkpiece.
 6. A method as defined in claim 5 wherein the workpiece isheated by contacting the workpiece with a heated gas.
 7. A method asdefined in claim 6 wherein the gas is nitrogen.
 8. A method as definedin claim 6 wherein the gas is ozone.
 9. A method as defined in claim 5wherein the workpiece is heated by contacting the workpiece with saidaqueous liquid maintained at an elevated temperature.
 10. A method fortreating a workpiece comprising the steps of: (a) depositing on thesurface of the workpiece a thin aqueous liquid boundary layer wherebyozone can diffuse through the boundary layer, and (b) contacting thesurface of the workpiece with ozone gas while the surface of theworkpiece is at an elevated temperature whereby the ozone reacts withthe surface of the workpiece by way of a diffusion-controlled reaction.11. A method as defined in claim 10 wherein the thin aqueous liquidboundary layer is established on the surface of the workpiece byspraying aqueous liquid onto said surface and rotating the workpiece ata speed of rotation sufficient to control the thickness of the boundarylayer.
 12. A method as defined in claim 10 wherein the thin aqueousliquid boundary layer is established on the surface of the workpiece bysupplying aqueous liquid in vapor form whereby the vapor condenses onthe surface of the workpiece to form a thin aqueous liquid boundarylayer thereon.
 13. A method as defined in claim 10 wherein the thinliquid boundary layer is established by spraying a mixture of ozone andaqueous liquid onto the surface of the workpiece whereby the ozoneseparates from said aqueous liquid as the aqueous liquid forms saidboundary layer.
 14. A method as defined in claim 10 wherein theworkpiece is maintained at an elevated temperature by heating theworkpiece.
 15. A method as defined in claim 14 wherein the workpiece isheated by contacting the workpiece with a heated gas.
 16. A method asdefined in claim 14 wherein the surface of the workpiece is maintainedat an elevated temperature by contacting the workpiece with said aqueousliquid at an elevated temperature.
 17. A method for treating a workpiececomprising the steps of: (a) spraying the surface of the workpiece withaqueous liquid while rotating the workpiece to form a thin aqueousliquid boundary layer on the surface thereof, said boundary layer beingsufficiently thin to permit ozone to diffuse therethrough, and (b)contacting the surface of the workpiece with ozone gas while the surfaceof the workpiece is at an elevated temperature whereby the ozone reactswith the surface of the workpiece by way of a diffusion-controlledreaction.